1. Field of the Invention
The present invention relates to a fluid shear coupling apparatus, and particularly to an apparatus having improved operational and maintenance features.
2. Description of the Prior Art
A variety of fluid shear couplings are known in the art and which typically include a driving member received within a working chamber defined by the driven member. Various, specific fluid shear surfaces and mounting means have been proposed. It is an object of the present invention to provide a fluid shear coupling apparatus which has improved operational and maintenance features over those of the prior art.
In U.S. Pat. No. 3,809,197, issued to Clancey on May 7, 1974, there is disclosed a viscous coupling including relatively rotatable input and output coupling members. These coupling members include a plurality of interdigitated lands and grooves which define a shear space therebetween and which are cooperable with viscous shear fluid in the shear space to transmit torque between the coupling members. A temperature-responsive valve means is included for controlling flow of viscous fluid from a reservoir chamber to the shear space. The output coupling member is mounted to a shaft of the input coupling member by means of ball bearings. A similar viscous coupling is disclosed in U.S. Pat. No. 3,856,122, issued to Leichliter on Dec. 24, 1974. The Leichliter coupling includes interdigitated lands and grooves defining a shear space between input and output coupling members. The Leichliter coupling is specifically designed to improve heat dissipation by means of the particular location of the shear surfaces and by the use of cooling fins rotating at the input speed to generate a greater blower action through the fins. Similar fluid shear couplings are disclosed in U.S. Pat. Nos. 3,498,431, issued to Sutaruk on Mar. 3, 1970; 3,323,623, issued to Roper on June 6, 1967; and 3,174,600, issued to Oldberg on Mar. 23, 1965.
In U.S. Pat. No. 4,004,668, issued to Blair on Jan. 25, 1977, there is disclosed a fluid shear coupling which includes pumping grooves extending across the concentric ridges or lands defining the fluid shear surfaces. These secant grooves extend across the top of the interdigitated ridges of the driving member and of the housing interior to cause the shear fluid to move generally radially for the purpose of inhibiting high temperature build-ups.
Depending upon the amount of the shear fluid in the drive chamber, the degree of rotary coupling between the driving member and the driven member is varied. This variance is usually controlled in the prior art by a temperature responsive valve assembly, the valve opening to admit a larger quantity of fluid to the drive chamber when high cooling requirements exist. Such assemblies often include a shear fluid passageway between the radially outermost portion of the drive chamber in which the drive rotor is positioned and the reservoir chamber. The shear fluid is deflected so as to flow from the radially outermost part of the drive chamber through the passageway back to the reservoir chamber.
One such device of this type is described in U.S. Pat. No. 4,007,819 to Maci on Feb. 15, 1977. In general, such devices lower the power lost to the radiator cooling fan by correlating the fan power requirement with the engine cooling requirement at various ambient temperatures.
In most temperature controlled, viscous fan drives currently manufactured, the change from partial engagement or coupling to full engagement occurs very rapidly upon the attainment of a certain activating air temperature. Upon actuation of the temperature responsive valve assembly, there is a sharp or sudden change in output speed between the partially engaged condition and a fully engaged condition. While such a characteristic may be desirable for many applications there are certain other applications, such as farm tractors, which operate more effectively and more efficiently with a modulated engagement. The term "modulated" is here used to denote a gradual, stable change in fan speed as a function of cooling system requirements, as distinguished from an abrupt or rapid change.